xe2x80x9cPriority is hereby claimed under 35 U.S. C. xc2xa7 119 to Australian Patent Application No. PS0408, filed Feb. 8, 2002, which is incorporated by reference in its entirety.xe2x80x9d
This invention relates to dragline dump position control and has been devised particularly though not solely to control the dumping position for a dragline that uses a differential hoist rope control for carry angle alteration.
When operating a dragline of the type described in international patent application PCT/AU00/01336, the content of which is incorporated herein by way of cross reference, there is a problem if an attempt is made by the operator to dump a payload within the bucket close in to the drag fairleads for the drag rope in that the bucket may not be able to reach its target dump angle due to the tension in the drag rope. In extreme cases, the angle reached may be insufficient to empty the bucket and this results in excessive slack in the front hoist rope which may become fouled and/or damaged. (Throughout this specification the term xe2x80x9cfront hoist ropexe2x80x9d is used to refer to the hoist rope attached to the front of the bucket i.e. adjacent the attachment point of the drag rope, and the term xe2x80x9crear hoist ropexe2x80x9d used to refer to the rope attached to the other or rear end of the bucket). In addition, when the slack is retrieved, excessive peak loads may be imparted to the hoist system components.
In a dragline using differential hoist rope control, it is highly desirable for the relative movements of the hoist ropes and the drag rope to be computer coordinated, and therefore also desirable to be able to control the dump position of the bucket by way of the computer control in order to ensure that any attempt to dump in an excessively close position is avoided.
It has been found however that the locus of points of the rear hoist rope hitch point which defines acceptable limits for a closest approach envelope in which to dump the bucket is a complex compound curve whose shape varies depending on many factors including bucket geometry, boom geometry and angle, boom sheave separation, rope load distribution and other parameters. The locus is typically a double cusp curve due to the complex rotation and translation mechanisms that occur during dumping at different levels above or below the drag fairleads. To attempt to analyse and control this complex curve during operation of a dragline so as to provide computer imposed limits on bucket position, or warnings to the dragline operator, requires a considerable amount of computational power and the programming of complex algorithms into the computer control system. This is undesirable due to cost implications and the necessity to make the computations in real time during the operation of the dragline.
It is therefore desirable to provide an alternative method of calculating when the bucket is reaching a position which may be too close in for efficient emptying of the bucket in a simple yet effective manner which is easy to implement using existing dragline controls and equipment.
Accordingly, the present invention provides a method of controlling the dump position of a dragline of the type wherein the inclination of the bucket is controlled by the differential control of two hoist ropes attached toward the front and the rear of the bucket respectively, said method comprising the steps of determining the radius of a cylindrical envelope having an axis coincident with the axis of rotation of the dragline house about its support base, calculating when the attachment point of the rear hitch rope of the bucket reaches said envelope and providing a signal for the control of the dump mode at that position.
Preferably the step of calculating when the attachment point of the rear hitch rope to the bucket reaches tie envelope, is performed by a computer in real time during the operation of the dragline.
Preferably the computer is the same computer used to control the differential payout of the front hoist rope and the rear hoist rope.
Preferably the radius of the cylindrical envelope is determined to approximate the locus of the positions of the attachment point of the rear hitch rope to the bucket at a predetermined carry angle of the bucket that will result in a predetermined dump angle when the front hoist rope is released.
Preferably the predetermined carry angle of the bucket is approximately +20xc2x0.
Preferably the predetermined dump angle is calculated to be the angle that will result in a substantial emptying of the bucket for a particular payload.
Preferably the predetermined dump angle is approximately xe2x88x9240xc2x0 or less.
Preferably the position of the attachment point of the rear hitch rope to the bucket is calculated using parameters from said same computer.
Preferably said parameters include rear rope inclination and rear rope payout values.